Looking at combo in Modern after Duskmantle Guildmage I see some great speculation targets that price out at $2 or less. Mindcrank is still available online for under sixty cents, and being the crucial piece of the potential combo makes that an easy double in my book.
Something as simple as Ghost Quarter can get the combo rolling, and this card will always have a home in very aggressive combo decks. With copies of Innistrad versions readily available for less than twenty-five cents, I imagine prices at least reach Dissension prices over time and I like the near term catalyst this combo and FNM Modern offer. Duress has seen many printings and while it likely fights Inquisition of Kozilek for a spot in any future decklists, I cannot suggest buying copies. As an easy throw in Duress is a great trade target, with player values for this staple all over the place.
Many avoid combo in Modern because many of the best tutors available in Magic have been banned in the format. Thankfully, transmute offers players plenty of cheaply costed tutors at 2cc. Muddle the Mixture offers some protection as well as fetching either a Guildmage or Mindcrank. Reasonably costed counterspell effects that double as tutors should be worth more than fifty cents. Shred Memory acts as another tutor and provides a bit of graveyard removal and at five cents has no where to go but up. Dimir Infiltrator rounds out a fetch package but its probably fully priced, at best it provides an aggressive price target for Shred Memory.
Tolaria West's transmute opens up several lines of play and brings the total tutor count to sixteen. While i like being able to pick up copies of playable out of print real estate at under $2, I think this card has a hard time getting as high as $3. Tolaria West also allows players to tutor up protection for their combo in the form of Pact of Negation. Pact has a high price point, but as combo gets better it should see more play. With copies readily available for less than $15, I think grinding out a 25% return on investment wouldn't be too hard here.
Echoing Truth looks good in any future Crank/Mage lists. It also looks good in light of some very annoying recently spoiled Gatecrash enchantments and artifacts. Buying copies for seventy-five cents or less and picking them up as throw ins offers another easy 25% return opportunity.
Gitaxian Probe is a great trade target right now. Trading into promo copies likely pays dividends over time and I like regular copies at fifty cents today. If Street Wrath can command a +$2 price point, the Probe should at least challenge that price.
Can Standard give players a combo deck to play with in the upcoming Gatecrash release? Undercity Informer has the potential to bring combo back in force. The ability to 4cc self mill to a land that dodges removal make Informant an uncommon worth picking up on the cheap. At worst Undercity Informer is another dredge card for Modern builds. Standard-focused Magic boards before a set release are very creative places, but an Undercity Informant, Burning-Tree Emissary, Fiend Hunter and Angel of Glory's Rise loop has legs, as activating the Informant before the combo is ready gets needed humans into the graveyard.
It's at least worth your time to hit up Dimir and Orzhov players after prerelease for their copies of Undercity Informer. Angel of Glory's Rise also looks like a decent sub $2 spec. Be sure to check out Mythic Spoiler's Guild Pack Viewer. It is a handy tool showing what possible cards can be pulled from each Guild Box.
With prerelease events just around the corner, the catalyst for these cards is looming. Remember to keep an eye out for power uncommons and commons as you play Gatecrash and happy hunting!